1. Field of the Invention
The present invention relates to a probe card, coaxial probes for the probe card, and a method of making them, which are used by a probe device for checking electric characteristics of semiconductor devices, for example. More particularly, it relates to a multi-pins and high density probe card of the vertical probe type (which will be hereinafter referred to as VTPC).
2. Description of the Related Art
A typical probe device is disclosed in Jpn. Pat. Appln. KOKAI Publication No. Sho 64-73632, for example. The probe card for this device has probes obliquely contacted with pads to be tested. As the semiconductor devices are made more highly integrated, however, the number of pads per chip is made larger and the pad is made smaller in size while the interval between the pads is also made smaller. The conventional probe card of the tilted probe type, therefore, cannot meet these semiconductor devices.
Instead of the probe card of the tilted probe type, therefore, a VTPC disclosed in Jpn. Pat. Appln. KOKOKU Publication Nos. Hei 2-28828 and Sho 63-28862 is now becoming practical. In this VTPC, the number of probes mounted can be increased to a greater extent and their mounting pitch can be made smaller.
In the VTPC, however, attention is paid not to characteristic impedance and shield quality of each probe but to making each probe super-slender and mounting a plurality of them on the probe card at a micro-pitch. Therefore, signal reflection is caused in the probe and cross talk (or a kind of noise) is caused between adjacent probes because the characteristic impedance of the probe is not matched with that of a tester. As the result, abnormal ringing is caused in signals transmitted to thereby add bad influence to the probing test.
A coaxial cable is more advantageous in that less noise enters into signals transmitted and that the characteristic impedance of the cable is stable. It is therefore expected that various kinds of merit can be obtained when the coaxial cable is used for wiring in the probe card. However, a peripheral conductor (such as the shield) of the cable must be earthed on a print plate but the print plate cannot produce any space for such earth connection.
The probe which has been shield-processed like the coaxial cable comes to have an outer diameter of about 0.8 mm. In a case where the print plate for the common VTPC is used, however, each pattern electrode to which the upper end portion of a probe member in each probe is soldered must be arranged on the print plate at a quite small pitch of about 1 mm-1.5 mm. It is therefore impossible from the viewpoint of space that an earth conductive layer (or ground) to which the upper end portion of an outer conductor (such as the shield) of each probe is soldered is formed on a same plane as the pattern electrodes and between them arranged at such small pitch, while keeping an insulating distance relative to them.
In a case where frequencies of test signals are in a high frequency region, signals are reflected and noise is caused when signals pass through those signal transmitting passages which have a characteristic impedance different from that of the tester. Therefore, characteristic impedances of probes through which signals are transmitted must be matched with that of the tester. In short, impedance matching must be carried out.